Yamaha YZ250(W)/W1 Owner's Service Manual page 236

CARBURETOR AND REED VALVE
4-9
EC466020
HANDLING NOTE
cC
Do not loosen the screws {TPS (throttle
position sensor)} except when changing
the TPS (throttle position sensor) due to
failure because it will cause a drop in
engine performance.
EC463000
REMOVAL POINTS
EC463110
Throttle valve
1. Remove:
9 Throttle valve 1
9 Ring 2
9 Spring (throttle valve) 3
9 Mixing chamber top 4
9 Throttle cable 5
NOTE:
While compressing the spring (throttle valve),
disconnect the throttle cable.
EC463401
Pilot air screw
1. Remove:
9 Pilot air screw 1
NOTE:
To optimize the fuel flow at a smaller throttle
opening, each machine's pilot air screw has
been individually set at the factory. Before
removing the pilot air screw, turn it in fully and
count the number of turns. Record this number
as the factory-set number of turns out.
ENG